1. Field of the Invention
This invention pertains to systems for applying electrical signals to an anatomical feature of a patient. While many of the disclosed concepts are applicable to a wide variety of therapies (e.g., cardiac pacing with electrodes applied to heart tissue), the invention is described in a preferred embodiment where the invention pertains to the treatment of gastro-intestinal disorders such as obesity, pancreatitis, irritable bowel syndrome and inflammatory disorders. In a most preferred embodiment, this invention pertains to the treatment of a gastrointestinal disorder by the application of a high frequency signal to a vagus nerve of a patient.
2. Description of the Prior Art
A blocking therapy can be used alone or in combination with traditional electrical nerve stimulation in which impulses are created for propagation along a nerve. The disorders to be treated include, without limitation, functional gastrointestinal disorders (FGIDs) (such as functional dyspepsia (dysmotility-like) and irritable bowel syndrome (IBS)), gastroparesis, gastroesophageal reflux disease (GERD), inflammation, discomfort and other disorders.
In a blocking therapy, an electrode (or multiple electrodes) is placed on or near a vagus nerve or nerves of a patient. By “near”, it is meant close enough that a field created by the electrode captures the nerve. As disclosed in the foregoing patent and applications, the electrode can be placed directly on a nerve, overlying tissue surrounding a nerve or on or in an organ near a nerve.
Higher frequencies (e.g., 2,500 Hz-20,000 Hz) are believed to result in more consistent neural conduction block. Particularly, the nerve conduction block is applied with an electrical signal selected to block the entire cross-section of the nerve (e.g., both afferent and efferent signals on both myelinated and non-myelinated fibers) at the site of application of the blocking signal.
In one embodiment of the electrodes a signal amplitude of 0.5 mA to 8 mA at the electrode-nerve interface has been found to be adequate for blocking. However, depending on electrode design, other amplitudes may suffice. Other signal parameters, as non-limiting examples, include an adjustable pulse width (e.g., 50 μsec to 500 μsec), and a frequency range of (by non-limiting example) 1000 Hz to 10,000 Hz. It must be recognized that the frequency sets certain limitations on the available pulse width; for example, the pulse width cannot exceed 50% of the cycle time for a symmetrical biphasic pulse.
A typical duty cycle of therapy could consist of 5 minutes on and 10 minutes off. These are representative only. For example, a duty cycle could be 2 minutes on and 5 minutes off or be 30 minutes on per day. These examples are given to illustrate the wide latitude available in selecting particular signal parameters for a particular patient.
A complete system for applying a signal to a nerve may include systems for addressing the potential for charge build-up, assuring good communication between implanted and external components, recharging implantable batteries, physician and patient controls and programming and communication with the system. These issues and selected prior art systems for addressing these issues will now be discussed.